The present invention relates to an improved method for preparing organopolysiloxane-polyoxyalkylene block copolymers, also referred to herein as siloxane-oxyalkylene copolymers, and to the compositions obtained thereby. More specifically, this invention relates to an improved hydrosilylation method for preparing siloxane-oxyalkylene copolymers consisting of one or more organopolysiloxane blocks bonded to one or more polyoxyalkylene blocks by one or more silicon-carbon bonds.
The preparation of siloxane-oxyalkylene copolymers by way of a hydrosilylation reaction between an organohydrogenopolysiloxane and an olefinically substituted polyoxyalkylene is well known. For one reason or another, such as to aid in handling the reactants or to moderate an exothermic reaction or to promote solubility of the reactants, the hydrosilylation reaction is typically conducted in a hydrocarbon solvent such as benzene, toluene or xylene. In these cases the hydrocarbon solvent is usually removed from the newly formed siloxane-oxyalkylene copolymer. This extra processing step is apparently done because the solvent is too flammable, or too toxic or otherwise unacceptable to be left in the copolymer. For example, see U.S. Pat. Nos. 2,846,458; 3,234,252; 3,280,160; 3,299,112; 3,402,192; 3,505,377; 3,565,845; 3,629,308; 3,657,305; 3,957,843 and 4,184,004. When it is desirable to have the hydrocarbon solvent mixed with the newly formed siloxane-oxyalkylene copolymer, including during the subsequent use to which the siloxane-oxyalkylene copolymer is directed, the hydrocarbon solvent need not be removed. See U.S. Pat. No. 4,381,241.
Less typically, the hydrosilylation reaction between the organohydrogenpolysiloxane reactant and the olefinically substituted polyoxyalkylene reactant is conducted in an oxygen-containing solvent such as an ether, a polyether or a lower alcohol.
For example, U.S. Pat. Nos. 3,280,160 and 3,402,192, noted above, also disclose the preparation of siloxane-oxyalkylene copolymers in n-butyl ether and in a 50/50 mixture of isopropyl alcohol/toluene, respectively. In addition, U.S. Pat. No. 4,122,029 discloses isopropyl alcohol as a suitable solvent for use in the preparation of siloxane-oxyalkylene copolymers. As in the cases where a hydrocarbon solvent was used these oxygen-containing solvents were also removed from the newly formed siloxane-oxyalkylene copolymer, presumably for the same general reason.
U.S. Pat. No. 3,629,308, noted above, also teaches that when one conventionally reacts an organohydrogenpolysiloxane with a polyoxyethylene having an allyl group on one end of the molecule and a hydroxyl group on the other in the presence of a platinum catalyst it is preferable to conduct the reaction in a suitable solvent to reduce the tendency of the newly formed siloxane-oxyalkylene copolymer to gel. Suitable solvents are said to include compounds having the formula R'O(C.sub.3 H.sub.6 O).sub.x H where R' is a lower alkyl group and x has a value from 1 to 20. When the resulting siloxane-oxyalkylene copolymer is to be used to stabilize a urethane foam, as disclosed therein, said patent teaches that it is not desirable to isolate the siloxane-oxyalkylene copolymer from such solvents but rather to use the solution thereof.